In recent years, as use of portable electronic devices (e.g., mobile phones and digital cameras) becomes ubiquitous, much effort has been put into reducing dimensions of portable electronic devices. Moreover, as dimensions of charged coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) based optical sensors are reduced, dimensions of imaging lenses for use with the optical sensors must be correspondingly reduced without significantly compromising optical performance. However, the most important characteristics of imaging lenses are imaging quality and size.
U.S. Pat. No. 8,477,431 discloses a relatively long conventional imaging lens that includes six lens elements, where both of the object-side surface and the image-side surface of the third lens element have a concave portion in a vicinity of a periphery of the third lens element. This design easily leads to a substantially undersized/small field of view which makes it difficult to comply with increasingly stringent design requirements.
Reducing the system length of the imaging lens while maintaining satisfactory optical performance is always a goal in the industry.